模拟SQLSERVER的两个函数：dateadd(),datediff()

//文件名：date.inc.php3
//在使用这两个函数前，要先将日期或日期时间转换成timestamp类型。
//如：
//$today=mktime(0,0,0,date("m"),date("d"),date("Y"));

/****模拟sqlserver中的dateadd函数*******
$part    类型：string
        取值范围：year,month,day,hour,min,sec
        表示：要增加的日期的哪个部分
$n        类型：数值
        表示：要增加多少，根据$part决定增加哪个部分
            可为负数
$datetime类型：timestamp
        表示：增加的基数
返回    类型：timestamp
**************结束**************/
function dateadd($part,$n,$datetime){
    $year=date("Y",$datetime);
    $month=date("m",$datetime);
    $day=date("d",$datetime);
    $hour=date("H",$datetime);
    $min=date("i",$datetime);
    $sec=date("s",$datetime);
    $part=strtolower($part);
    $ret=0;
    switch ($part) {
        case "year":
            $year+=$n;
            break;
        case "month":
            $month+=$n;
            break;
        case "day":
            $day+=$n;
            break;
        case "hour":
            $hour+=$n;
            break;
        case "min":
            $min+=$n;
            break;
        case "sec":
            $sec+=$n;
            break;
        default:
            return $ret;
            break;
    }
$ret=mktime($hour,$min,$sec,$month,$day,$year);
    return $ret;
}

/****模拟sqlserver中的datediff函数*******
$part    类型：string
        取值范围：year,month,day,hour,min,sec
        表示：要增加的日期的哪个部分
$date1,$date2    类型：timestamp
        表示：要比较的两个日期
返回    类型：数值
**************结束*(*************/
function datediff($part,$date1,$date2){
    //$diff=$date2-$date1;
    $year1=date("Y",$date1);
    $year2=date("Y",$date2);
    $month2=date("m",$date2);
    $month1=date("m",$date1);
    $day2=date("d",$date2);
    $day1=date("d",$date1);
    $hour2=date("d",$date2);
    $hour1=date("d",$date1);
    $min2=date("i",$date2);
    $min1=date("i",$date1);
    $sec2=date("s",$date2);
    $sec1=date("s",$date1);

    $part=strtolower($part);
    $ret=0;
    switch ($part) {
        case "year":
            $ret=$year2-$year1;
            break;
        case "month":
            $ret=($year2-$year1)*12+$month2-$month1;
            break;
        case "day":
            $ret=(mktime(0,0,0,$month2,$day2,$year2)-mktime(0,0,0,$month1,$day1,$year1))/(3600*24);
            break;
        case "hour":
            $ret=(mktime($hour2,0,0,$month2,$day2,$year2)-mktime($hour1,0,0,$month1,$day1,$year1))/3600;
            break;
        case "min":
            $ret=(mktime($hour2,$min2,0,$month2,$day2,$year2)-mktime($hour1,$min1,0,$month1,$day1,$year1))/60;
            break;
        case "sec":
            $ret=$date2-$date1;
            break;
        default:
            return $ret;
            break;
    }
    return $ret;
}

} 

原文转自：http://www.ltesting.net